Prior fuel injection systems which may be used with, for example, diesel engines, have typically been of the pump-line-injector type or the unit injector type. A pump-line-injector fuel injection system includes a main pump which pressurizes fuel to a high level, e.g., on the order of about 103 to 138 MPa (about 20,000 p.s.i.), and individual fuel injectors which are coupled by fuel supply lines to the pump. In a unit injector system, a low-pressure pump delivers fuel to a plurality of unit injectors, each of which includes means for pressurizing the fuel to a relatively high value, again on the order of about 103 to 138 MPa (about 15,000 to 20,000 p.s.i.) or greater.
In both types of injection systems, each injector conventionally includes a check having a tip which is biased by a spring against a valve seat. When fuel is to be injected into an associated engine combustion chamber, pressurized fuel is admitted into an injector cavity within the injector. When the fuel pressure in the cavity overcomes the spring force exerted on the check, the check is lifted, thereby spacing the check tip away from the valve seat and permitting pressurized fuel to escape into the associated engine combustion chamber through one or more injector nozzle orifices.
While conventional injection apparatus of the foregoing type have been useful to control the admittance of pressurized fuel into an associated engine combustion chamber relative to approximately top dead center (TDC), such apparatus is only indirectly controlled, i.e., the motive force for moving the injector check is provided by the pressurized fuel itself rather than a directly controllable motive power source. Accordingly, the degree of controllability required to desirably reduce particulate emissions in accordance with regulatory agency standards is lacking.
While there may be fuel injectors designed for spark-ignition engines which have a directly-operated check, Applicants are unaware of any successful designs for a fuel injector having a directly-operated check for a diesel-cycle engine or where high fuel injection pressures (e.g., greater than about 6.9 MPa or 1000 p.s.i.) are required.